The transport in containers of perishable goods, in particular of foods, requires the maintenance of temperatures in accordance with the ATP rules and in particular with Class A, for products designated “fresh”, with temperatures that, in relation to the type and mode of transport or distribution, are comprised between 0° C. and +4° C. or between 0° C. and +7° C., and with Class C, with temperatures below −18° C., for products designated “frozen”. Containers of perishable goods are typically means that require high standards of preservation of the goods they contain, ensuring autonomous thermal preservation without intermediate recharging for periods as long as 30 days.
In particular, containers can be divided into two main categories, on the basis of the inner length/inner height ratio of the container, and a distinction is made between containers in which such ratio is greater than 1.5 or smaller than 1.5.
Containers with an inner length/inner height ratio greater than 1.5 can be used for preservation and transport of perishable goods:                up to 5-7 days mainly for short sea, intermodal, and off-shore transport (hereinafter “short sea”);        up to 12-15 days for multimodal transport, river navigation, and small and medium coastal navigation (hereinafter “mid sea”);        up to 30 days for deep sea transport (hereinafter “deep sea”).        
Containers with an inner length/inner height ratio of up to 1.5 are instead used for the preservation and transport of perishable goods over short and medium distances, and particularly for off-shore, on-shore, intermodal and road transport, as well as in “short sea” shipping.
In conventional containers for perishable goods, maintenance of a controlled temperature regime is achieved either by way of the application of heat accumulation systems, or by way of the use of electromechanical refrigeration systems which are powered electrically or by Diesel generators.
Both of the aforementioned technologies are not devoid of drawbacks, however.
Conventional heat accumulation systems have several unresolved technical problems, which are described below.
a) Heat accumulation systems comprise box-like modules containing a heat accumulation liquid that is subject to volumetric dilation owing to the phase transition of the liquid. In the box-like modules there are volumes that are not filled with liquid, which contain a vacuum and are used as an expansion chamber. If the container is not perfectly leveled, then the outflow at one end of the heat accumulation liquid will result in the total filling of a part of the module where dilation with no possibility of expansion during freezing of the liquid will cause destructive levels of pressure. Furthermore the presence at one end of tubular connections with limited exchange surface leads to the formation of significant pockets of liquid which subsequently freeze with further localized formation of destructive levels of pressure and the breakage within a short time of the box-like modules.
b) The limited heat exchange capacities of conventional heat accumulation systems involve the necessity of covering, in order to obtain the necessary exchange surfaces, most of the walls with the above mentioned box-like modules, with consequent increase in the costs and tare weight of the container. Covering the floor is of particularly critical importance, since it is subject to major stresses. Furthermore the limited heat exchange capacities must be compensated with higher-powered systems, with consequent increase in losses of charge and thus in energy consumption.
c) The arrangement of the box-like modules of conventional heat accumulation systems is thermally discontinuous, in particular in the upper corners of the container which are exposed to solar radiation and where the principal thermal bridges are located. This results in significant thermal flows with consequent thermal loads that have to be absorbed by the internal part of the heat accumulation system.
d) The thermal load inside the container is not uniform but is concentrated on the roof by way of the solar radiation, the thermal flows deriving from the lack of thermal continuity, and the metabolic heat of the fruit and vegetable products preserved inside the container. Such non-uniformity results in a reduction in autonomy, an increase in the tare weight and in transport costs.
e) The box-like modules in conventional heat accumulation systems are hung from the ceiling of the container by way of polyurethane panels, which, under the effect of the weight of the heat accumulation modules, the vibrations, and the episodes of acceleration experienced during the transport and handling of the container, tend to become detached, rendering the container unusable.
f) The box-like modules, made of aluminum, do not allow the use of saline solutions for the heat accumulation liquid, since they are not compatible with aluminum and in any case they are unstable over time.
g) It is currently not possible to use conventional accumulation systems in containers for perishable products belonging to Class C, but these are used for Class A product only, where the thermal loads are significantly lower.
h) An intrinsic characteristic of all means of transport, in particular for medium and long trips where many pallets are loaded by way of mechanical means, is the difficulty of sanitization and the introduction of significant bacterial loads during loading, with consequent exponential growth thereof, as well as the formation of Botrytis and other mildews, as well as the difficulty of generating and maintaining a modified atmosphere that minimizes the metabolism of the products after loading in the container.
Conventional technology based on refrigeration apparatuses depends on a continuous electric or Diesel-electric power supply with mains power in ports, on board ship, and aggregated Diesel generators on lorries for road stages, and it has the drawbacks described below.
a) The refrigeration assembly is generally installed at one end of the container which can be over 13 m in length with an internal cross-section of 4.8 m2, completely filled with products, where the available cross-sections for the circulation of air for the delivery are very small and require high air circulation speeds, greater than 12 msec. The interaction between the high air circulation speed and the small cross-sections available have the following drawbacks:                high losses of charge with associated high absorptions of energy;        an increase in the coefficient of deterioration of the preserved products, and an increase in desiccation, even with high relative humidity and optimal temperature;        the formation of ice and the necessity of frequent defrosting;        the high speed of the air in contact with the walls, ceiling and upper corners brings an increase in the thermal flow between the environment and the container interior, in particular at the thermal bridges, doors etc.;        
b) The refrigeration assemblies require a significant maintenance cost, not least because maintenance operations can be carried out only by specialist technicians in special-purpose service centers.
c) The refrigeration assemblies are not adapted for use on rail transport, on ships without mains sockets, in particular for river navigation and small and medium coastal navigation, on lorries without Diesel generators, for post-harvest refrigeration, and in all cases where energy is not continuously available.
d) The refrigeration apparatuses do not make it possible to conform to the requirements for the optimal preservation of fresh products, i.e. absence of ventilation, humidity over 95% and temperature constantly at optimal values.
e) The refrigeration capacity is limited to the maintenance of products only, and does not make it possible to carry out the post-harvest refrigeration of products.
f) The use of conventional refrigeration systems is not permitted for the provisioning of off-shore oil platforms and for transit in very long tunnels, where the use is required of intrinsically safe electrical systems and therefore it is necessary to use complex procedures that require shutdown on approach, adjacent to platforms and in tunnels, with consequent interruption of refrigeration and increase in running costs.